1. Field of the Invention
The invention relates generally to imaging systems and more particularly to three dimensional imaging systems for use in nuclear medicine.
2. Description of Background Art
Multiple gamma ray cameras often are used in nuclear medicine to generate high quality three dimensional images for clinical studies such as brain studies, heart studies, total body, bone and other diagnostic studies, using SPECT (Single Photon Emission Computed Tomography), or PET (Positron Emission Tomography). One challenge in this field is to provide a three dimensional imaging apparatus for multiple cameras and/or camera movements to allow for high patient throughput for both economic and therapeutic reasons. Diagnosis cost is reduced if more patients can be tested per unit time. For very ill patients or patients in intensive care the time for image acquisition should be minimized in the interests of patient health and comfort.
Accordingly, a variety of gantries, gamma detector types and detector orbital movements have been exploited. Modern gamma ray cameras utilize detectors, such as Anger cameras, that have a wide field of view to allow imaging the full width of the body of a patient at each angular view or stop without requiring rectilinear scanning. These detectors generally use thick lead collimators to acquire projection data. The collimators often are positioned close to the patient to generate high resolution images. The image data acquired by the detectors are processed by a computer to reconstruct a tomographic image. Techniques for processing image data are well-known and described, for example, in “Principles of Instrumentation in SPECT” by Robert Eisner, Journal of Nuclear Medicine, Vol. 13, #1, Mar. 1985, pp. 23-31; Computed Tomography in Nuclear Medicine” by John Keyes, (chapter in) Computer Methods, C. V. Mosley, St. Louis, 1977, pp. 130-138; and “Single Photon Emission Computed Tomography,” by Bernard Oppenheim and Robert Appledown, (chapter in) Effective Use of Computers in Nuclear Medicine, Michael Gelfand and Stephen Thomas, McGraw-Hill Book Co., New York 1988, pp. 31-74.
To facilitate faster detection time, dual-head systems with detectors oriented at a fixed angle of 180°, and triple-head systems, with three detectors oriented at fixed angles of 120° have been used, particularly for SPECT gamma ray imaging. Further, detectors on a gantry may rotate about the patient, thereby defining a lateral axis as the mechanical axis of rotation aligned with a computer matrix for reconstructing the SPECT images.
Acquisition of data for a total body scan typically involves movement of detector(s) along the patient's body and dual head or triple head systems allow shortened time via simultaneous data capture. However, high quality images require angular sampling of data over typically at least 180 degrees around the focal point of an imaging apparatus. Thus, a high-quality SPECT for brain, bone, or liver studies for example, generally requires a view taken along a complete 360 degree circle (360° scan) around the body of the patient. Typically, about 64 to 128 angular views or stops are required to acquire the image data, using a single detector. For cardiac SPECT imaging, typically at least 32 stops over a 180 degree arc about the patient's body (180° scan) may be required.
Generally, rotating gantries are used that move detector(s) within an orbit, allowing multiple positions for the same detector(s). See, for example, U.S. Pat. Nos. 6,242,743; 5,757,006, and see U.S. Pat. Nos. 4,652,759; 4,652,758; 4,645,933, 6,184,530 and 4,613,122, the contents of which are incorporated by reference in their entireties. Unfortunately, large rotating gantries in particular, such as that described in U.S. Pat. No. 6,184,530, generally require heavy drive gear rings and other parts and tend towards large gantries, which makes the overall apparatus quite large and less open to the patient.